1. Field of the Invention
The present invention relates to a pump apparatus and, more particularly, to a pump apparatus capable of obtaining a high discharge pressure with a low driving pressure and is used when seawater or dirty water is allowed to pass through a semipermeable membrane, e.g., a reverse osmosis membrane to obtain drinking water.
2. Description of the Related Art
As shown in FIGS. 8 and 9, a conventionally known pump apparatus (e.g., JP-B 3-21208 (1991)) of this kind comprises a pump body 100 having a cylinder 101 and a plunger 102, a manual lever (not shown) which allows the plunger 102 to reciprocate in the cylinder 101, a filter (reverse osmosis membrane) 130, a suction passage 103 which sucks liquid (seawater or dirty water) from outside into a pumping chamber 100a of the pump body 100, a sending-out passage 104 for sending out the liquid in the pumping chamber 100a to the filter, a supply passage 131 for flowing, to outside, the water which was purified through the filter 130, a circulation passage 105 for circulating condensed water which did not pass through the filter 130, into a driving chamber 100b of the pump body 100, a discharge passage 106 for discharging the condensed water outside from the driving chamber 100b, and a switching valve (cross valve) 110 which switches a communication state with respect to the driving chamber 100b toward the circulation passage 105 or the discharge passage 106. This conventional pump apparatus can rock the manual lever with a slight force utilizing a liquid pressure of the condensed water generated at the time of pumping operation. In FIGS. 8 and 9, dotted arrows show a direction of flow of fluid, and arrows A and B show reciprocating direction of the plunger 102.
The switching valve 110 includes a cylindrical hole 111 formed in a manifold (not shown) which covers an outside of the pump body 100, a shuttle 112 accommodated in the cylindrical hole 111 and provided at its outer peripheral surface with a pair of first recessed peripheral groove 112a and second recessed peripheral groove 112b, a plug 113 which liquid-tightly seals an end opening of the cylindrical hole 111, a rod shaft 114 which penetrates the plug 113 and which is connected to one end of the shuttle 112, and a button 115 mounted on one end of the rod shaft 114. Formed between the pump body 100 and the manifold are a first flow-in passage 116 for allowing a portion of liquid in the pumping chamber 100a to flow into a first chamber 111a formed on a deep side within the cylindrical hole 111, a second flow-in passage 117 for allowing a portion of condensed water in the driving chamber 100b into a second chamber 111b formed on the side of the rod shaft 114 in the cylindrical hole 111, and a communication passage 118 which switches a communication state between the circulation passage 105 and the discharge passage 106 through one of the pair of recessed peripheral grooves 112a and 112b by means of the reciprocation operation of the shuttle 112. A flow-out hole 105a of the circulation passage 105 is in communication with the first recessed peripheral groove 112a of the shuttle 112, and the discharge passage 106 is in communication with the second recessed peripheral groove 112b. A reference numeral 121 represents an intake valve, a reference numeral 122 represents a discharge valve, and a reference numeral 123 represents a relief valve.
A basic operation when liquid is sent out by this conventional pump apparatus (JP-B 3-21208 (1991)) will be briefly explained. The manual lever is rocked to move the plunger 102 of the pump body 100 up (in the direction of the arrow B) from a state shown in FIG. 8 to a state shown in FIG. 9 toward one end of the pump body 100. With this operation, liquid flows into the pumping chamber 100a through the suction passage 103 from outside. On the other hand, if the plunger 102 is moved down (in the direction of the arrow A) from the state shown in FIG. 9 to the state shown in FIG. 8, the liquid is sent to the filter 130 through the sending-out passage 104 from the pumping chamber 100a, and a portion of the liquid which passed through the filter 130 flows out as purified drinking water through the supply passage 131. At that time, a portion of the liquid in the pumping chamber 100a flows into a second chamber 111a of the switching valve 110 through the first flow-in passage 116, pushes and moves the shuttle 112, switches the first recessed peripheral groove 112a and the communication passage 118 into the communication state, and condensed water which is remaining liquid and which did not pass through the filter 130 passes through the circulation passage 105, the first recessed peripheral groove 112a of the switching valve 110 and the communication passage 118 and is circulated into the driving chamber 100b. A liquid pressure of this circulated condensed water cooperates with a force applied to the manual lever to move the plunger 102 down. That is, since a pressure existing in the pump system is balanced, the pumping operation can be carried out only by adding a slight force to the manual lever. Thereafter, if the plunger is again moved up (in the direction of the arrow B), the condensed water in the driving chamber 100b flows into the second chamber 111b of the switching valve 110 through the second flow-in passage 117, the shuttle 112 is moved by the liquid pressure, the second flow-in passage 117 and the discharge passage 106 are switched to the communication state through the second recessed peripheral groove 112b, and the condensed water in the driving chamber 100b is discharged out.
In the case of this pump apparatus, however, when the pumping operation is started, air in the driving chamber 100b is discharged and liquid is smoothly sucked into the pumping chamber 100a. Therefore, it is necessary to carry out the following operation. That is, the button 115 is pressed by a finger (at a pressure of about 1.06 kg/cm2 (15 psi), the shuttle 112 is forcibly moved to the deep end of the cylindrical hole 111 to close the flow-out hole 105a of the circulation passage 105 and to open the discharge passage 106 (see FIG. 9), and air in the driving chamber 100b must be discharged into the discharge passage 106 through the communication passage 118 and the second recessed peripheral groove 112b of the switching valve 110. This button-pressing operation is an adjusting operation required until the pump apparatus functions normally, and it is necessary to continue this operation until the liquid flows out from the discharge passage 106 and air in the pump system is discharged in some degrees (until a pressure of about 5.62 kg/cm2 (80 psi) is generated). That is, if the pump system is filled with liquid, the shuttle 112 reciprocates (switching of the switching valve 110 normally functions) in the cylindrical hole 111 with appropriate timing by a liquid pressure generated by the reciprocating movement of the plunger 102, and condensed water normally flows into the driving chamber 100b and is normally discharged from the driving chamber 100b. However, in an initial state of the pumping operation, since air exists in the pump system, the internal pressure (liquid pressure) in the driving chamber 100b is insufficient and a frictional resistance in a dry state is caused between the shuttle 112 and the cylindrical hole 111. For this reason, the shuttle 112 can not easily move to the deep side in the cylindrical hole 111, and since the switching valve 110 can not switch with appropriate timing, air can not be discharged. There is a structural cause that since a passage for flowing fluid into the driving chamber 100b and for discharging fluid from the driving chamber 100b is the single communication passage 118, the fluid reversely flows through the communication passage 118 immediately after the flow-in and flow-out are switched by the switching valve 110, and the fluid can not flow easily.